1. Field of the Invention
This invention generally pertains to the field of interior lighting and more particularly relates to an electromechanical color control system for linear fluorescent lamps, particularly for use in accent or mood lighting.
2. State of the Prior Art
It is known that people respond at a subconscious level to changes in color and intensity of ambient illumination. For example, slowly dimming light which also changes from white light through increasingly deep shades of blue to darkness is perceived as an end-of-day or nightfall time, bringing about a change in mood conducive to relaxation and eventual sleep. Conversely, a slow increase in illumination from darkness shifting through deep yellow through increasingly brighter shades of yellow to full white light brings about a gradual, natural arousal of a sleeping or resting individual to a state of wakefulness in a manner analogous to waking in response to daybreak and sunrise. These subliminal responses are deeply ingrained in the human and indeed the animal physiology as a result of long evolution, and such changes in illumination are more gentle and harmonious than abrupt turning on or off of interior lights. These benefits have been recognized and exploited in lighting systems of various types, ranging from movie theater lighting to waking clocks equipped with room light controls. These benefits have also been recognized by the airline industry, and efforts have been made to equip passenger aircraft with centrally controlled accent lighting systems for providing a more natural transition in cabin Illumination between daytime and nighttime conditions, and thereby facilitate the passengers transition from wakefulness to sleep and back to wakefulness during long flights.
Effective mood lighting calls for control over both light color and intensity. Color control of artificial lighting under electronic control has been developed particularly by theater/stage lighting equipment manufacturers largely using incandescent light sources. Strips or sheets of colored film are scrolled in front of the light source, and the film transmits only the color of interest. Motorized spools are used to pull scrolls made up of successive sheets of different colored film to achieve a desired sequence of colors. Particular colors can be selected by electronic control of the spools.
Fluorescent lamps have a different shape or form factor than incandescent lamps, in that the former have linear shapes while the latter are doser to point sources of light. The linear fluorescent lamps or tubes produce light by means of an arc discharge in a partially evacuated glass tube. The arc discharge results in emission of certain wavelengths which in themselves are not desirable for general illumination. The interior of the glass tube is coated with a fluorescent compound which emits white light when subjected to the arc discharge emissions. Fluorescent lamp tubes have an elongated shape in order to achieve a sufficient light emitting area along the tube, because the intensity of light emitted by a short tube is usually inadequate for interior lighting. Recently, so called compact fluorescent lights have become available, consisting of long, small diameter fluorescent lamp tubes bent to a compact shape. However, many applications remain for straight fluorescent lamp tubes of various lengths and diameters.
Airliners make extensive use of linear fluorescent lamps for cabin illumination and no simple, effective and economical system for controlling color of linear light sources is available. Scrolling rolls of colored film between two spools in front of a fluorescent tube is not a practical solution for mood or accent lighting applications. In one alternate approach, multiple lamp tubes of different colors are provided, and the net color output is controlled by adjusting the relative light intensity of the various tubes. This approach requires three lamp tubes with separate ballasts for controlling power to each of the tubes and is therefore costly, complex and weighs more than a single tube solution. It is also difficult to diffuse and blend the different colors into a homogeneous white light. In an effort to alleviate these shortcomings, another approach uses white fluorescent lamps in combination with colored light emitting diodes (LEDs). As the white lamp tube is dimmed the appropriate combination of colored LEDs is powered up to provide the desired effect. This approach is deficient in that the LEDs are expensive and not very bright yet consume considerable power, separate power supplies are required for the lamp tube and the LEDs, the different colored light sources are hard to diffuse into even illumination, and the quality of white light is compromised.
A continuing need exists for simpler color control of linear fluorescent lamps.
This invention addresses the aforementioned need which provides a variable color linear fluorescent lamp suitable for accent or mood lighting of aircraft cabin interiors and other interior lighting applications. The variable color lamp has a lamp base on which is mounted a lamp tube between opposite end sockets, and a color tube supporting a number of colored filter strips each disposed longitudinally along the color tube and in circumferentially adjacent relationship to each other. The color tube is supported for rotation about the lamp tube, and a motor is provided for rotating the color tube. A mask defines an aperture for limiting light emission by the lamp fixture only to light filtered by a selected circumferential portion of the color tube. A color control system is operatively connected to the motor for selectively positioning the color tube in relation to the aperture thereby to select the desired coloring of light emitted from the lamp housing.
The mask may be interposed between the color tube and the lamp tube. Alternatively, the mask may be positioned exteriorly to the color tube. The filter strips are preferably of even width with each other, and may be each of a single color, which color may vary in color density across a strip width.
In one form of the invention adapted for simulation of nightfall and daybreak illumination at least one of the filter strips is substantially opaque to transmission of light and at least one other of the strips is substantially clear. One or more colored filter strips are circumferentially interposed between the opaque and the clear strips. The colored strips may comprise a yellow filter strip and a blue filter strip, preferably of graduated density and increasing in density from the clear filter strip towards the substantially opaque strip.
The filter strips may be affixed to the tube with an adhesive, by a shrunk wrapper or by printing onto a surface of the tube. The filter strips may be, for example, gel filter strips or dichroic filter strips. In some cases it may be desirable to provide an ultra violet filter interposed between the filter strips and the lamp tube.
The color control system is operative for rotating the color tube from the initially selected dear filter to the opaque filter passing through at least one colored filter strip and then again to the dear filter passing through a second colored filter strip at a relatively slow rate not readily perceptible to a human observer thereby to achieve slow changes in intensity and color of illumination suggestive of nightfall and daybreak.
In one particular application, this invention discloses a method for simulating daybreak and nightfall ambient illumination comprising the steps of providing a linear fluorescent lamp including a lamp tube, providing a lamp aperture for emitting light from the lamp tube into an illuminated environment, and filtering light emitted through the aperture through filter media of gradually changing density of color suggestive of nightfall and daybreak respectively between blocked and unfiltered conditions of the emitted light The step of filtering light comprises selectively rotating a number of light filters including a substantially clear filter, a substantially opaque filter, a yellow filter and a blue filter, into alignment or registry with an aperture arranged for limiting emission of light to light filtered through a selected portion of the filter media, comprising one or more of the light filters. In a presently preferred embodiment the yellow filter and the blue filter are each interposed between the clear filter and the opaque filter over the circumference of a cylindrical color tube rotatable about a concentrically supported lamp tube, and wherein the yellow filter and the blue filter are each of increasing density from the clear filter towards the substantially opaque filter.
In an alternate form of the invention, mechanical dimming of a linear fluorescent tube is achieved by dispencing with the color filter strips of the color tube and providing a dimming tube which is clear with only an opaque longitudinal strip of sufficient circumferential dimension to substantially block emission of light when the opaque strip is brought into registry with the mask aperture. Initial positioning of the dimming tube so as to align only the clear portion with the mask aperture allows substantially unimpeded passage of light emitted by the lamp tube and full intensity illumination by the light fixture. Rotation of the dimming tube gradually and increasingly brings the opaque strip into partial registry with the mask aperture, thereby blocking light emission to an increasing extent. When the opaque strip is brought into full registry with the mask aperture light emission is substantially fully blocked and the lamp fixture is in a dark state although the lamp tube is turned on. Between the full illumination and dark states of the lamp fixture close, precise control of light intensity is readily achieved by rotational positioning of the dimming tube.
These and other improvements, features and advantages will be better understood by reference to the following detailed description of the preferred embodiment and the accompanying drawings.